<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #box{
            color: aliceblue;
            width: 110px;
            height: 25px;
            border: 1px solid #c5c5c5;
            border-radius: 10px;
            background-color: #797777;
            text-align: center;
            /* text-indent: 5px; */
            font-size: 14px;
            line-height: 25px;
            cursor: pointer;
        }
        #down{
            border: 1px solid #c5c5c5;
            width: 90px;
            margin-left: 5px;
            display: none;
        }
        ul{
            padding: 0;
            margin: 0;
        }
        li{
            list-style: none;
            font-size: 14px;
            border-bottom: 1px dashed #c5c5c5;
            text-align: center;
            height: 25px;
            line-height: 25px;
            color: aliceblue;
            background-color: #333;
            cursor: pointer;
        }
        li:hover{
            background-color: #5c0e0e;
        }
    </style>
</head>
<body>
    <div id="box">请选择手机名称</div>
    <div id="down">
        <ul class="phones">
            <li>华为</li>
            <li>小米</li>
            <li>oppo</li>
            <li>vivo</li>
            <li>爱疯</li> 
            <li>三星</li>
        </ul>
    </div>
</body>
</html>
<script>
        var obox = document.getElementById("box");
        var odown = document.getElementById("down");
        var oli = document.querySelectorAll("li");
        console.log(oli);
        var timer;
        //当点击obox时，呈现出下拉列表的内容，给个延时效果
        obox.onclick = function(){
            clearInterval(timer);
            timer = setInterval(function(){
                odown.style.display = "block";
            },300)
            ///选中列表中的某一项并将其呈现在box中,隐藏下拉列表
            for(var i=0;i<oli.length;i++){
                oli[i].n = i;
                oli[i].onclick = function(){
                    obox.innerHTML = this.innerHTML;
                    odown.style.display = "none";
                    clearInterval(timer);
                }
            } 
        }
</script>